Swath printers/plotters are in widespread use today for printing many types of images. A printing system suitable for a printer is described in U.S. Pat. No. 5,745,137, which employs off-carriage ink reservoirs connected to on-carriage print cartridges through flexible tubing. The off-carriage reservoirs continuously replenish the supply of ink in the internal reservoirs of the on-carriage print cartridges (or "printheads" or "pens"), and maintain the back pressure in a range which results in high print quality. While this system has many advantages, there are some applications in which the relatively permanent connection of the off-carriage and on-carriage reservoirs via tubing is undesirable.
An ink delivery system (IDS) for printers has been developed, wherein the on-carriage reservoir of the print-head is only intermittently connected to the off-carriage reservoir to "take a gulp" and is then disconnected from the off-carriage reservoir. No tubing permanently connecting the on-carriage and off-carriage elements is needed. The above-referenced related applications describe certain features of this "take a gulp" ink delivery system.
When an inkjet printer starts a print using a multi-pass print mode, the top of the page is printed with just a few nozzles of the printheads, the print medium is advanced a short distance, a few more nozzles are printed, and the print medium is again advanced a short distance, and so on. When the printer is printing normally during a print or plot using a multi-pass print mode, there are several partially formed swaths (groups of rows of pixels) with some pixels printed, and others not yet printed. At the end of a plot, the printer completes all pixels of all rows before stopping.
The take-a-gulp system as well as other large scale plotters can be employed to print large color images, wherein significant volumes of the colored inks can be used from the on-carriage reservoirs during a given print. The system includes the capability of tracking the ink volume spent from one or more of the on-board ink reservoirs and thus providing a measure of the ink remaining, and detecting when a reservoir needs refilling. If this occurs while printing, and the system were to invoke a refill operation as if doing a normal pen servicing, the carriage would be moved to the service/refill station, even though the plot is not completed, and the refill operation performed. A problem is that this interruption in printing leaves the image drying for a relatively long period of time, perhaps several minutes, before printing is resumed to complete the plot. In some print media, this action creates an arti-fact, a visible horizontal band all across the page, at the area at which printing was interrupted for the refill. Additionally, the printheads cool off during this pause, and water evaporates from the printhead nozzles, which can result in different print performance when printing resumes.
There was no solution to this problem. In other platforms, printing was continued until the cartridge ran out of ink and then the machine canceled the plot. Other possible outcomes included a very visible artifact resulting from printing interruption, or not completing the print, or printing the image with a white gap and perhaps missing some information.
It would therefore represent an advance in the art to provide a technique for reducing artifacts resulting from mid-plot-pausing.